FIG. 7A is a structural cross sectional view of a hydrogen filling port for a car in 70 MPa specifications described in SAE J2799.
As illustrated in FIG. 7A, the hydrogen filling port has a connector structure in which seal members are arranged in a receptacle 1 as a reception side. A first O-ring 3 which has a larger diameter is assembled at an insertion port 2 side through which a nozzle (not illustrated) is inserted. Further, a pair of backup rings 4a, 4b and a second O-ring 5 are arranged at a back side apart from the insertion port 2 along a center line. The second O-ring 5 has a smaller outer diameter and is arranged between a pair of backup rings 4a, 4b. 
The pair of backup rings 4a, 4b and the second O-ring 5 are assembled in a fixing groove 6 as an annular groove which has a smaller diameter than an inner diameter of the insertion port 2. Further, an annular partition 7 which projects toward an inner diameter side is formed between the first O-ring 3 and the pair of backup rings 4a, 4b, the second O-ring 5 at the back side.
Further, for example, Patent Literature 1 discloses a gas supply structure as this kind of connector structure which has a first O-ring arranged near an insertion port of a receptacle, a second O-ring arranged at a downstream side of the first O-ring, and a foreign body removal member which is arranged between the first O-ring and the second O-ring.